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CVE-2026-97688— urllib3: Chunked Deflate streaming can enter an infinite loop

Quick assessment

Affected
urllib3 urllib3
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedl

CVSS 6.9 · Medium
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I. Basic Information for CVE-2026-97688

Vulnerability Information

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Vulnerability Title
urllib3: Chunked Deflate streaming can enter an infinite loop
Source: CVE Program / CVE List V5
Vulnerability Description
urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedly decodes them without progress. The issue occurs when an untrusted server sends a chunked Deflate response whose decoded body exceeds a positive finite chunk size and whose encoded body has trailing bytes, specifically a response with Transfer-Encoding: chunked and Content-Encoding: deflate, content decoding enabled, and the positive finite amt=N streaming chunk size. The attack mechanism is that a malicious server returns a compressed chunked response with trailing bytes after the Deflate stream. The impact is excessive CPU usage and a request that does not complete, and network read timeouts do not interrupt the loop because no further socket read occurs. This issue is fixed in version 2.8.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
不可达退出条件的循环(无限循环)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
urllib3 urllib3 >= 2.6.2, < 2.8.0 -

II. Public POCs for CVE-2026-97688

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III. Intelligence Information for CVE-2026-97688

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Other References for CVE-2026-97688 (3)

Same Patch Batch · urllib3 · 2026-09-29 · 3 CVEs total

CVE-2026-97689 8.9 HIGH urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into me
CVE-2026-97687 7.6 HIGH urllib3: HTTPS proxy TLS configuration may be ignored or overridden

IV. Related Vulnerabilities

Same product: urllib3
Same vendor: urllib3
Same weakness: CWE-835

V. Comments for CVE-2026-97688

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